Compact soft X-ray source for biological applications

A compact soft X-ray source with carbon nanotubes (CNTs) based field emission electron source is being developed for applications to biological, medical and material technology fields. In the tests using a diode-type source, the maximum current of 13 mA (density of over 50 mA/cm/sup 2/) was extracted from the CNTs emitters (0.26cm/sup 2/) at electric field of about 6 V//spl mu/m and 2.5 /spl times/ 10/sup -5/ Pa pressure. In addition, a triode-type source was designed to obtain a pencil-like soft X-ray beam. Geometrical parameters in the source were optimized using calculation codes for electric fields and electron beam orbits. The X-ray source was stably operated, and the electron beam current of 0.24 mA was obtained at the applied anode voltage of 35 kV. Based on the numerical estimations, it is expected that the focal size is about 0.5 mm, and the X-ray beam density is 1.5/spl times/ 10/sup 7/ photons/s with the divergence angle of 30 mrad.